Label-free coherent anti-stokes Raman scattering imaging of coexisting lipid domains in single bilayers.

Laser-scanning coherent anti-Stokes Raman scattering (CARS) microscopy was used to image lipid domains in single bilayers without any labeling. On the basis of the molecular packing density difference between liquid-disordered (Ld), liquid-ordered (Lo), and gel (So) phases, clear vibrational contrasts were generated between coexisting domains in a single bilayer of DOPC/DPPC (1:1) and DOPC/DPPC/cholesterol (4:4:2). The method reported here can be potentially applied to study phase segregation in live cell membranes which are highly heterogeneous and dynamic.